I never worked with stored procedures myself, sorry... But I believe you can use CALL SQL statement just like SELECT in report data queries.
If it works in TDataQuery, it must work in Report Workshop as well.

About avoiding using UI

User interface is not necessary, you can create reports in code.
We have several demo projects showing how to create reports in code. For example, for FireDAC, all numbered demo projects in Demos\FireDAC\

I do not understand the problem with reportDocpProperties. What do you mean? There is TRVReportDocObject class, it is required to store document-related report properties, for example a data query applied to the whole document. But using this object directly is not required. For example, you can use RVReportSetRootDataQuery function to define the data query to apply to the whole document.